My suggestion is to first check with the school and see if they have recommendations on what they prefer students to use, etc.
I just bought mine the other day. I stuck to my local stores and found that for the most part a manual cuff is a manual cuff. I did try to go the cheaper route before and ended up with this one that was almost plastic and I was scared it would pop while in use... needless to say it was returned. Walmart had a manual cuff... but you have to be careful because they came with the steth already attached and positioned so you did not learn positioning.
I think things to look for... and this depends on how much you are willing to spend as well... are cuff size... If you think that you will be working with people with larger arms or children you have to take into consideration using the wrong size cuff will alter the B/P reading. There are sets online that have the bulb, guage, and different cuffs. Getting an adult cuff and one for larger arms would probably be most helpful to you if you can find a good set. Or else... since the majority of people can use the normal adult size just stick with that. The other thing is that you want to make sure that you are getting a nylon type cuff that you can wipe down with an alcohol wipe (and yes... some schools
will make you clean off the school cuffs after each clinical day)
Otherwise, in my searching, it seemed there were different brands but they were all basically the same thing. If you wanted a particular color or were looking for a pattern then they seemed to be priced just a tad higher...